Time-base circuit for cathode-ray tube



y 3, 1965 1'. POORTER 3,195,009

TIME-BASE CIRCUIT FOR CATHODE-RAY TUBE Filed July 16, 1962 4 Sheets-Sheet 1 TEUNIS PCDRTER July 13, 1965 T. POORTER 3,195,009

TIME-BASE-CIRCUIT FOR CATHODE-RAY TUBE Filed July 16. 1962 4 Sheets-Sheet 2 INVENTOR TEUNIS POORTER AGEN July 13, 1965 1'. POORTER TIME-BASE CIRCUIT FOR CATHODE-RAY TUBE 4 Sheets-Sheet 3 Filed July 16, 1962 FIG.7

FIG.8

INVENTOR TEUNIS POORTER Za f.

AGENT TIME-BASE cmcfim FOR CATHODE-RAY TUBE Filed July 16, 1962 4 Sheets-Sheet 4 INVENTOR TEUNI S POOR'I'E R United States Patent M 3,195,099 TIME-BASE ClRCUiT FOR CATHODE-RAY TUBE Tennis Poorter, Emmasingel, Eindhoven, Netherlands, assignor to North American Philips Company, Inc New York, N.Y., a corporation of Delaware Filed July 16, 1962, Ser. No. 209,982 Claims priority, application Netherlands, Aug. 17, 1961,

9 Claims. (Cl. 315-27) This invention relates to time-base circuit arrangements of the kind employing a semi-conductor switching device wherein a sawtooth current is generated in a cathode-ray tube deflection coil during the non-conductive state of said switching device and wherein energy isfed back to the supply source during the said non-conductive state.

Time bases of the kind set forth have been described in US. Patent No. 2,995,679 and it is an object of the invention to obtain an improved circuit arrangement of the said kind.

Such so-c-alled flyback-driven circuit arrangements produce a sawtooth currentth-rough a coil and comprise a DC. voltage source, a supply impedance, a capacitor, a transformer to which the deflection coil is coupled, a switching device and a recovery diode. A charging current, supplied from the DC. voltage source via the supply impedance to the capacitor, accumulates electrical energy in the capacitor. The switching device is rendered conductive by means of a control signal during the flyback period of the sawtooth current, as a result of which the electrical energy accumulated in the capacitor is converted, in the form of a current through the switching device, into magnetic energy accumulated in the field of the transformer and the coil coupled to it. By virtue of the circulated energy, the diode coupled to the transformer is automatically rendered conductive during the stroke period of the sawtooth current and means are present to cut off the switching device as a result of which the magnetic energy accumulated in the field can flow back to the DC. voltage source in the form of a current through the recovery diode.

However, the known circuit arrangement has the drawback that the core material of the transformer is subject to considerable premagnetisation. This is due to the fact that the energy derived from the D.C. voltage source is first accumulated in the capacitor, then flows during the flyback, into the field of the transformer and the coil coupled to it, and, during the stroke, flows back into the source of direct voltage via the diode, so that the supply of energy occurs via a first path and the recovery via a second path. Since in the known circuit the return of the energy accumulated in the field of the transformer takes place exclusively via the diode connected to the said transformer, it will be clear that the current which is produced by this recovery of energy only flows in one direction and will therefore contain a considerable D.C. component, as a result of which the core material of the transformer will be premagnetized.

This is undesirable because a greater amount of core material has to be used because, due to the premagnitization, the steep part of the magnetic flux density-magnetic field strength (B-H)-character-istic of the core material cannot be used so that a smaller variation of the magnetic flux density (AB) is avail-able. As a result of this the proportions of the core and/or the copper volume have to be greater than when there is no premagnetization. This also results in increased leakage and losses within the transformer.

In addition, where the coil through which the saw-tooth current produced is flowing is the horizontal deflection coil in a television receiver, it is normal to step up the pokes produced across the transformer winding during the 3,195,0fi9 Patented July 13, 1965 fiyback period of the sawtooth current and to rectify and use them for supplying EHT to the final anode of the picture tube and/or for supplying the focusing voltage for said tube. However, this requires increased energy, resulting in a further increase in the size of the transformer because in the known circuit the current through the transformer which flows back to the DC. voltage source through the diode is responsible for the energy recovery. If the recovered energy becomes less (greater beam cur rent in the picture tube) the current through the transformer winding and through the diode will be less. This current, however, must not become zero before the stroke period of the sawtooth current is terminated, otherwise the sawtooth waveform is deformed. From this it follows that in a circuit which also supplies the EHT, the premagnetization must be greater in the initial adjustment (beam current zero) than Without.

The object of the invention is to provide a flybackdriven circuit arrangemet of the kind referred to hereinbefore in which no premagnetization of the core material occurs or if such a premagnetisation is permitted so that the arrangement delivers additional energy to a varying additional load the premagnetisation is counteracted by this additional energy.

In order to realize this, the flyback-driven circuit arrangement according to the invention is characterised in that at least three windings are provided on the transformer core. The first winding, having a number of turns n is traversed by the current which supplies electrical energy to the capacitor and is traversed in the opposite sense by the current which recovers the magnetic energy accumulated in the field to the DC. voltage source. The second winding, having a number of turns n is exclusively traversed by the charge current of the capacitor, and the third winding, having a number of turns n is traversed by the discharge current of the capacitor or by the discharge current of the capacitor plus the current which returns the magnetic energy to the DC. voltage source. All three windings are wound in the same sense on the core of the transformer, while the number of turns 11 and 11 are chiefly determined by the ratio between the flyback period and total period of the sawtooth current, and the total number of ampere turns of the transformer can be made as small as possible by means of the numbers of turns n n and 11 In order that the invention may readily be carried into effect, some possible embodiments of flyback-driven circuit arrangements according to the invention will now be described by way of example with reference to the accompaying drawings, in which FIG. 1 shows a somewhat modified form of the known circuit employing a silicon rectifier as the possible switch ing device. The said rectifier will be hereinafter referred to as an S.C.R.,

FIG. la is the symbol for a n-p-n-p S.C.R. and FIG. 1b shows the symbol for a p-n-p-n S.C.R.,

FIG. 2 is a first embodiment of a circuit according to the invention,

FIGS. 3, 4, 5 and '6 are the stages to come from the known circuit arrangement according to the invention,

FIG. 7 shows the magnetic flux density magnetic field strength (B-i-D- characteristic to indicate the variation of the premagnetization of the circuit arrangement as shown in FIG. 2 is also used for producing the E.H.T. for a picture tube in a television receiver,

FIG. 8 is a similar embodiment as shown in FIG. 2 but includes a recovery capacitor as the auxiliary D.C. voltage source,

FIG. 9 shows a second embodiment of a circuit arrangement according to the invention,

FIG. 10 is a modified embodiment of the invention with respect to FIG. 9.

FIG. 1 shows a somewhat modified circuit as that known from the US. Patent 2,995,679. The circuit is provided with an auto-transformer and with an overswing coil L so as to cut oh the SCR marked T, used in this circuit as the switching device, after termination of the flyback. The purpose of the overswing coil L which may also be used if alternatively a transistor is employed as the switching device, which purpose is of no significance for the present invention. Therefore, the object of the coil L will not be further described.

The S.C.R. marked T shown in FIG. 1 is of the n-p-n-p type the emitter e of which consists of n-material, the base b of p-material and the collector 0 also of p-rnaterial, while a layer consisting of n-material is provided between the base and the collector. The current in such a S.C.R. is directed from the collector c to the emitter e. Its symbol is shown in FIG. 1a.

Alternatively a p-n-p-n S.C.R. may be used. In such a S.C.R., the current flows from the emitter e to the collector c. The symbol for this latter S.C.R. is shown in FIG. 1b. It will be clear that if a p-n-p-n S.C.R. is used instead of a n-p-n-p S.C.R. the polarity of the source of supply voltage and of the diode D must be reversed.

In the circuit shown in FIG. 1, L is the supply coil, 1 a DC. voltage source capable of supplying a direct voltage of V volts, 2 an autotransformer to the tapping 3 of which one terminal of a capacitor C is connected, the other terminal being connected to the junction point of the supply coil L and the overswing coil L The defiection coil L is connected to the secondary 4 of the transformer 2. The sawtooth current to be produced flows through the coil L and this coil may consequently be provided around the neck of a television picture tube, if the circuit is used in a television receiver, or around the neck of a camera tube, if the circuit is used in a television camera. The coil L in this case serves as a deflection coil for the horizontal deflection of the electron beam of the tube. However, it will be clear that also magnetic deflection of an electron beam in a cathode ray tube of a cathode ray oscillscope is also possible With the present circuit. It has already been stated and will be explained hereafter that electrical energy is accumulated in the capacitor C which is accumulated as magnetic energy in the field of the transformer 2 and the coil L coupled to it during the flyback period via the S.C.R. marked T which is then conductive and which is rendered conductive at the beginning of the fiyback period by the pulsatory control signal 7 applied through the capacitor 5 and the resistor 6. The accumulated field energy is returned to the source 1 via the diode D which is conductive during the stroke period. It follows from the above that the current which returns the field energy to the source 1 only flows via the winding of the transformer 2, as a result of which the core material of this transformer is strongly premagnetized even if no, or nearly no, losses would occur.

In order to avoid this premagnetisation, according to the invention the transformer winding 8 must be divided into at least three windings which have to be traversed by the various currents in a particular manner. This is shown in FIG. 2, in which the winding 8 is divided into windings 8 and 8" which are magnetically coupled together and to the winding 4. The winding 8 is again divided into two windings 11 and n so that a total of three windings are present, namely the windings n n and 8".

In order to explain the operation of the circuit shown in FIG. 2, reference is made to FIG. 3 in which the known circuit of FIG. 1 is shown in a somewhat modified manner and in which the S.C.R. marked T and the diode D are represented as switches T and D, while the source 1 is omitted and the equivalent direct voltage of V, volts produced by this source is shown instead. The capacitor C is charged during the stroke period of the sawtooth current 3 by a current i which during the stroke period which the switch T is opened is equal to the current i supplied via the supply coil L At the beginning of the flyback period, the switch T is closed and the direction of i is reversed so that the capacitor C discharges and its electrical energy is accumulated as magnetic energy in the field of the transformer 2 and the deflection coil L coupled thereto. During the flyback period the switch D is opened so that the current i flows as a current i through the overswing coil L and the switch T to the part of the winding 8 between the tapping 3 and earth. The current i through this part of the winding during the fiyback consequently equals i while i =i i While observing that the current i during the flyback flows in a direction opposite to that indicated by the arrow in FIG. 3.

At the end of the fiyback the voltage at the junction point of the diode D and the winding 8 assumes such a value as a result of the sinusoidal discharge current i that diode D becomes conductive and in effect the witch D is closed. At the same instant the switch T is opened. The magnetic energy which was accumulated in the field is returned to the source 1 in the form of a current i via diode D. At the same time, the direction of the current 1' is again reversed and this current flows in the direction indicated by the arrow, as a result of which capacitor C is charged. Since the current i through capacitor C will on an average be zero, it follows that a mean current will flow through the left branch formed by the coils L and L and the switch T which, if no losses occur, will be equal to the mean current through the right hand branch formed by the winding 8 and the switch D. This latter mean current causes the premagnetisation of the core material of the transformer 2.

A first stage in the process of arriving at the circuit arrangement of the invention is shown in FIG. 4. In this figure, the winding 8 of the transformer 2 is divided into two windings 8' and 8" which are magnetically coupled together. Between these two windings the switch D is provided, while the terminal of the capacitor C connected to the transformer 2 is connected to the junction point of switch D with winding 8". The operation of the circuit as shown in FIG. 4 is the same as that shown in FIG. 3, but this first stage is necessary in order to understand the second stage shown in FIG. 5, in which the end A of the supply coil L is shifted from the positive supply terminal to the junction point of the switch D with winding 8".

In the circuit shown in FIG. 5, the premagnetisation has already considerably been improved. For, the paths for the energy supplied and returned are partially combined in the winding 8', so that the current I namely the mean current through the winding 8, equals zero if no losses occur in the circuit. In this case I =I I in which T is the mean current through the branch formed by the supply coil L the overswing coil L and the switch T and I is the mean current through the winding 8 and the switch D. Since the mean current I ensures the supply of energy via the instantaneous currents i 1' and i and the mean current I ensures its return via the instantaneous currents i and i then I =T in the absence of losses. Therefore, the mean current I through the winding 8' will not contribute to the premagnetisation of the core material of the transformer 2.

However, there is still a premagnetization effect due to the mean current I through the winding 8". In order to remove this latter premagnetisations effect, a third stage is necessary as shown in FIG. 6. In this stage the winding 8 is again divided into two windings m and n and the junction point of diode D with the winding 8' is shifted to a tap-ping 9 between windings 11 and 12 In as far as the mean current T through winding n is concerned the situation has not changed as compared with that shown in FIG. 5. In FIG. 6 it also holds that T =T -T and, if the circuit has no losses T =T so that T =0 from which it follows that the current I which flows through the winding n will cause no premagnetisation.

Since the current T flows through the winding n in a direction opposite to that of the current T through the winding 8", it Will be clear that no premagnetisation will occur in the transformer if n T =n T in which 11 is the number of turns of the winding n and 11 the number of turns of the winding 8" and if the windings n and 8" are wound on the transformer 2 in the same sense. Assuming no losses 11:2 and it follows that n =n In practice losses will occur and the recovered energy will be smaller than the supplied energy.

From this it follows that T2 3 so that also In this case it may be ensured that the premagnetisation becomes Zero by choosing the number of turns n n and 11 of the windings n 11 and 8" respectively so that T n +T n T n 0 From Equation 3 plus Equations 1 and 2 it follows n n The transformer ratio "a "fl-. 3

is established, an additional degree of freedom is available by the presence of the winding n which may be used to preadjust the premagnetisation at will. Naturally, also another adjustment than that indicated by the Equation 3 may be obtained.

For example, if in case that the circuit as shown in FIG. 2, which with the exception of the part for producing the high voltage V is identical to that shown in FIG. 6, is a deflection circuit in a television receiver for the horizontal deflection of the electron beam in the picture tube, also the EHT supply V for the picture tube is to be derived from the circuit shown in FIG. 2; an additional winding 10 should be provided on the transformer 2 to which a rectifier 11 is connected which rectifies the pulses which are produced during the fiyback period AT and are stepped up by the winding 10, so that an EHT V is obtained which is supplied to the final anode of the picture tube. As a result of this additional energy requirement the losses occuring in the circuit increase with increasing electron current. The adjustment may be chosen so that holds, likewise with n n if no high voltage load is present, that is to say with beam current zero. In this case the core material is premagnetised to one side of the magnetic flux density magnetic field strength (3-H)- characteristic as indicated by point B in FIG. 7. If a larger beam current flows the mean current I increases and the mean current I decreases because less energy is recovered. As a result of this, also the current T =T T 5 increases, so that the adjustment indicated by the Equation 3a changes into that indicated by the Equation 3. If the adjustment of the number of ampere turns is chosen so that the adjustment indicated by the Equation 3 occurs at the average beam current, the adjustment of the transformer 2 will change into in the case of a beam current greater than the average current, so that the core material is premagnetised to the other side of the (3-H) characteristic.

If the premagnetisation, which may occur when the maximum possible beam current flow is chosen in the point E shown in FIG. 7 the average beam current occuring will just cause no premagnetisation. As a result of this the extreme limits B and E will be more favourable than when for a zero beam current, the adjustment had been adjusted in the origin of the B-H- characteristic. For, in that case with maximum beam current the core material might become saturated, as a result of which the sawtooth current produced would be distorted.

Another embodiment of the circuit arrangement shown in FIG. 2 is shown in FIG. 8. This circuit operates in exactly the same manner as that shown in FIG. 2. However, in this circuit a recovery capacitor 1" is provided across which a voltage V is developed so that the total supply voltage for the circuit is equal to V +V where V is the voltage supplied by the actual DC. voltage source 1'.

In fact, the capacitor 1" which has such a large capacitance value that the voltage V developed across it does substantially not vary as a result of the charge and dis charge currents flowing through it, takes the place of the source 1 of FIG. 2 and the source 1' serves exclusively for compensation of the losses occuring in the circuit. This is easy to see. For, if no-losses occur, the source 1 may be omitted and the junction point of the capacitor 1" with the winding 8" must be connected to earth. Then, again the circuit shown in FIG. 6 is obtained, in which the DC. voltage source 1 is replaced by a recovery capacitor 1" to be considered as an auxiliary D.C. voltage source. In this latter case, the number of turns n 11 and 11 of the arrangement shown in FIG. 8 are equal to those shown in FIGS. 2 and 6. If losses do occur, the source 1 is strictly necessary and also the number of turns n 11 and 11 will differ from those of FIGS. 2 and 6.

FIG. 9 shows another embodiment of a circuit according to the invention. In this circuit, the winding 13 is the first winding which is traversed by the current which supplies the electrical energy to the capacitor C and is traversed in opposite sense by the current which returns the magnetic energy accumulated in the field of the transformer 2 and the coil L via the diode D into the source 1. The current i' flowing through the winding 13 with number of turns n' consequently has a mean valve 5 which will be zero if no losses occur and will have a value deviating from zero in the event of losses.

The winding 14 is coupled magnetically to the winding 13 so that it may be assumed that these windings belong to the transformer 2. The Winding 14 is again divided into two windings with number of turns n' and It' Thus transformer 2 in FIG. 9 again comprises three windings, in which the winding 13 is the first winding, the winding with number of turns n' is the second winding and the winding with number of turns n';, is the third winding. The second winding is traversed by the charge current i' for the capacitor C and the third winding by the disformer 2 with number of turns n' and the winding 14" is the third winding with number of turns n The current i' in FIGS. 9 and 10 will deviate from current i in FIGS. 2 and 8, since the third Winding in FIGS. 9 and 10 is only traversed by the discharge current i' of the capacitor which accumulates the electrical energy from the capacitor C as magnetic energy in the field. If the S.C.R. marked T is cut off, i becomes zero, while in the circuit shown in FIGS. 2 and 8 the current i remains flowing, during the stroke period, via the third winding 8 and the diode D back to the first winding 8 and the source 1, or the capacitor 1", respectively.

Now magnetic energy accumulated in the field during the stroke period can flow back to the source 1 only via the first winding 13 and the diode D. Hence, the numbers of turns n' 22' and n' deviate from the numbers of turns n n and n from FIGS. 2 and 8 but in this case the ratio n /n' is again chiefly a function of the ratio between the flyback period At and the total period time T of the sawtooth signal produced.

If no losses occur it also holds for the circuit of FIGS. 9 and 10 that i' namely the mean value of the charge current 2' equals 5' namely the mean value of the discharge current 7' Since in this case it also holds that T =T T so that T will be zero when no losses occur, and n' =n' This means that the tapping 15 in FIG. 9 on the second winding 14 is shifted to the junction point of the winding 14 with the overswing coil L If losses do occur, T ='I' -T' 0 and T T so that when the premagnetisation of the core material must be zero.

As shown in FIG. 9, in this case also the high Voltage V for the picture tube can, in a simple manner, be produced by providing an extended winding to which the rectifier 11 is connected. In this case also for zero beam current the number of ampere turns of the transformer 2 may be chosen according to the equation T It' +T' n' -T' n O likewise with n' n' in a manner such, that for the average beam current through the picture tube the adjustment according to Equation 40 changes over into that according to the Equation 4 in a corresponding manner as described for the circuit shown in FIG. 2.

It will be clear that, in addition to the embodiments described, also other circuits can be realized according to the principle of the invention. The essential feature is that the transformer used comprises at least three windings which are wound on the core in the same sense. The three winding feature is quite apart from other windings, such as for example, the windings 4, 10 and 1t) which are provided on the transformer 2 for coupling purposes.

As previously described above, the transformer 2 is first of all required to establish an exact equilibrium condition between charge and discharge time of the capacitor C in connection with the ratio between stroke and flyback period. This is eifected by the transformer ratio n /(n -i-n for FIGS. 2 and 8 and n' /n' for the circuit of FIGS. 9 and 10 respectively. Owing to the presence of three windings the choice of the number of turns 11 and n respectively is free so as to satisfy at will the Equations 3, 3a, 4 or 4a.

It will be clear that these conditions can be satisfied also in the case of another configuration of the circuit. For example, the first winding with the number of turns n n respectively need not always be one winding. It may be divided into two windings with the same number of turns and the same winding sense, in which the current which charges the capacitor C flows through one winding and the current returned via the diode D flows through the other of those divided windings.

In addition it is noted that it is to be preferred to give the supply coil L an inductance value which is as large as possible. In that case a substantially constant charge current i or 1" respectively is obtained, which, in connection with the energy passed round is the most favourable situation since in this case the fewest losses occur.

What is claimed is:

1. A deflection circuit for producing a sawtooth current in a deflection coil, said sawtooth current having a stroke period and a fiyback period, comprising a source of direct voltage, a transformer having a core and first, second and third windings wound thereon in the same sense, the number of turns of said first and third windings being determined by the ratio between the flyback period and the total period of said sawtooth current, means coupling said defiection coil to a portion of said transformer, switching means having a control terminal for controlling conduction thereof, a capacitor, an impedance element and a diode, means connecting said first and second windings, said impedance element and said capacitor to said voltage source thereby establishing a charge current path from said source to said capacitor by means of said first and second windings, means for coupling a control signal to said control terminal of said switching means to render said switching means conductive during said fiyback period, means connecting said switching means in circuit with said capacitor and said third winding so as to provide a discharge path for said capacitor through said third Winding whereby the energy accumulated on said capacitor is coupled to said transformer and said deflection coil and converted into magnetic energy which is stored in the fields thereof, means for cutting off said switching means thereby rendering said diode conductive during said stroke period, means connecting said diode to said first winding so as to provide a current path through said diode by which the magnetic energy accumulated in the transformer field is returned to said voltage source as a current fiow through said first winding in a direction opposite to the direction of capacitor charge current flow through said winding, said last named connecting means and said diode further providing a shunt path around said second winding which prevents the current flow produced by the return of energy from said transformer field from flowing through said second winding, the number of turns of said second winding being chosen such that bias magnetization of said transformer core is substantially compensated.

2. Apparatus as described in claim 1 wherein the energy losses are substantially constant and wherein the number of turns of the three windings are chosen such that the value of the sum of the ampere turns produced in windings one and two caused by the mean currents I and 1 respectively, flowing therein, are substantially equal to the ampere turns produced by the mean current 1 flowing in said third winding, and wherein said mean current I in winding one is equal to the difference in the mean currents I and I flowing in windings 2 and 3, respectively, and wherein the number of turns of winding 3 is greater than the number of turns of winding 2.

3. Apparatus as described in claim 1 wherein said deflection coil is adapted for use with a television picture tube for deflecting the electron beam, and further comprising a rectifier coupled to said transformer for deriving the high direct voltage for said picture tube whereby energy losses in said circuit increase with an increasing beam current, said first, second and third windings being arranged such that the sum of the ampere turns produced by the mean current 1 flowing in winding one and the mean current 1 flowing in winding 2 is less than the ampere turns produced by the mean current 1 flowing in Winding 3 at low values of electron beam current and wherein said mean current I in winding one is equal to the difference in the mean currents l and i flowing in windings 2 and 3, respectively, and wherein the number of turns of Winding 3 is greater than the number of turns of winding 2.

4. Apparatus as described in claim 3 wherein the number of turns of windings one, two and three are arranged to produce a net bias ma netization of the transformer core in a first direction at zero electron beam current and a net bias magnetization of said core in the opposite direction for the maximum value of eiectron beam current.

5, Apparatus as described in claim 4 wherein the magnetic field strengths produced in the core material are substantially equal and opposite for zero beam current and maximum beam current in said picture tube.

6. A deflection circuit for producing a sawtooth current in a deflection coil, said sawtooth current having a stroke period and a fiyback period, comprising a source of direct voltage, a transformer having a magnetic core and first, second and third windings wound thereon in the same sense, means coupling said deflection coil to a portion of said transformer, a diode, means connecting said first winding, said diode and said third winding in series, in the order named, across said voltage source, an impedance element and a capacitor, means connecting said second winding, said impedance element and said capacitor in series circuit in the order named, said connecting means further comprising means for connecting said series circuit in parallel with said diode, said first and second windings and said impedance element forming a charge current path for said capacitor thereby to accumulate an electric charge thereon, switching means having a control terminal for a control signal, means connecting said switching means in circuit with said capacitor and said third Winding so as to provide a discharge path for said capacitor through said switching means and said third winding, means for coupling said control signal to said control terminal of said switching means thereby to render said switching means conductive to close said discharge path and initiate said fiyback period, means for initiating said stroke period by cutting-oii said switching means and rendering said diode conductive thereby providing a current path by means of said diode and said first Winding through which the energy accumulated in the transformer field during said fiyback period is returned to said voltage source during said stroke period, said diode being poled so that the current flow through said first winding :during the stroke period is in the opposite direction to the current flow therein during the accumulation of charge on said capacitor, said diode providing a shunt path which prevents the current flow produced by the return of energy from said transformer field from flowing through said second winding.

'7. Apparatus as described in claim 6 wherein the number of turns of windings one and there are determined by the ratio between the fiyback period and the total period of the sawtooth current and the number of turns of winding 3 is greater than the number of turns of winding 2.

8. A deflection circuit for producing a sawtooth current in a deflection coil, said sawtooth current having a stroke period and a fiyback period, comprising a source of direct voltage, a transformer having a magnetic core and first, second and third windings Wound thereon in the same sense, means coupling said deflection coil to a portion of said transformer, a diode, means connecting said first winding and said diode in series circuit across said voltage source, an impedance element and a capacitor, means connecting said impedance element, said second winding and said capacitor in series circuit, in the order named, and further connecting said series circuit in paraiiel with said diode, one terminal of said capacitor and diode forming a junction and means connecting said junction point to one terminal of said voltage source, said first and second windings and said impedance element forming a charge current path for said capacitor thereby to accumulate an electric charge thereon, switching means having a control terminal for a control signal, means connecting said switching means in a closed circuit with said capacitor and said third winding so as to provide a discharge path for said capacitor through said switching means and said third winding, means for coupling said control signal to said control teminal of said switching means thereby to render said switching means conductive to close said discharge path and initiate said flyback period, means for initiating said stroke period by cutting-off said switching means and rendering said diode conductive thereby providing a current path by means of said diode and said first winding through which the energy accumulated in the transformer field during said fiyback period is returned to said voltage source during said stroke period, said diode being poled so that the current flow through said first winding during the stroke period is in the opposite direction to the current fiow therein during the accumulation of charge on said capacitor, said diode providing a shunt path which prevents the current fiow produced by the return of energy from said transformer field from flowing through said second winding.

9. Apparatus as described in claim 8 wherein the number of turns of windings one and three are determined by the ratio between the fiybaok period and the total period of tie sawtooth current and the number of turns of winding 3 is greater than the number of turns of winding 2.

References Cited by the Examiner UNITED STATES PATENTS 2,924,745 2/60 Janssen 31527 DAVID G. REDINBAUGI-I, Primary Examiner.

ROBERT SEGAL, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,195,009 July 13, 1965 Tennis Poorter It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 19, for "arrangemet" read arrangement column 4, line 14, for "i read i l line 70, for "premagnetisations" read premagnetisation column 7, line 25, for "-T read l column 9, line 51, for "there read three Signed and sealed this 19th day of July 1966.

isEAL Attest:

QSRNEST w. SWIDER EDWARD J. BRENNER Lttesting Officer Commissioner of Patents 

1. A DEFLECTION CIRCUIT FOR PRODUCING A SAWTOOTH CURRENT IN A DEFLECTION COIL, SAID SAWTOOTH CURRENT HAVING A STROKE PERIOD AND A FLYBACK PERIOD, COMPRISING A SOURCE OF DIRECT VOLTAGE, A TRANSFORMER HAVING A CORE AND FIRST, SECOND AND THIRD WINDINGS WOUND THEREON IN THE SAME SENSE, THE NUMBER OF TURNS OF SAID FIRST AND THIRD WINDINGS BEING DETERMINED BY THE RATIO BETWEEN THE FLYBACK PERIOD AND THE TOTAL PERIOD OF SAID SAWTOOTH CURRENT, MEANS COUPLING SAID DEFLECTION COIL TO A PORTION OF SAID TRANSFORMER, SWITCHING MEANS HAVING A CONTROL TERMINAL FOR CONTROLLING CONDUCTION THEREOF, A CAPACITOR, AN IMPEDANCE ELEMENT AND A DIODE, MEANS CONNECTING SAID FIRST AND SECOND WINDINGS, SAID IMPEDANCE ELEMENT AND SAID CAPACITOR TO SAID VOLTAGE SOURCE THEREBY ESTABLISHING A CHARGE CURRENT PATH FROM SAID SOURCE TO SAID CAPACITOR BY MEANS OF SAID FIRST AND SECOND WINDINGS, MEANS FOR COUPLING A CONTROL SIGNAL TO SAID CONTROL TERMINAL OF SAID SWITCHING MEANS TO RENDER SAID SWITCHING MEANS CONDUCTIVE DURING SAID FLYBACK PERIOD, MEANS CONNECTING SAID SWITCHING MEANS IN CIRCUIT WITH SAID CAPACITOR AND SAID THIRD WINDING SO AS TO PROVIDE A DISCHARGE PATH FOR SAID CAPACITOR THROUGH SAID THIRD WINDING WHEREBY THE ENERGY ACCUMULATED ON SAID CAPACITOR IS COUPLED TO SAID TRANSFORMER AND SAID DEFLECTION COIL AND CONVERTED INTO MAGNETIC ENERGY WHICH IS STORED IN THE FIELDS THEREOF, MEANS FOR CUTTING OFF SAID SWITCHINMG MEANS THEREBY RENDERING SAID DIODE CONDUCTIVE DURING SAID STROKE PERIOD, MEANS CONNECTING SAID DIODE TO SAID FIRST WINDING SO AS TO PROVIDE A CURRENT PATH THROUGH SAID DIODE BY WHICH THE MAGNETIC ENERGY ACCUMULATED IN THE TRANSFORMER FIELD IS RETURNED TO SAID VOLTAGE SOURCE AS A CURRENT FLOW THROUGH SAID FIRST WINDING IN A DIRECTION OPPOSITE TO THE DIRECTION OF CAPACITOR CHARGE CURRENT FLOW THROUGH SAID WINDING, SAID LAST NAMED CONNECTING MEANS AND SAID DIODE FURTHER PROVIDING A SHUNT PATH AROUND SAID SECOND WINDING WHICH PREVENTS THE CURRENT FLOW PRODUCED BY THE RETURN OF ENERGY FROM SAID TRANSFORMER FIELD FROM FLOWING THROUGH SAID SECOND WINDING, THE NUMBER OF TURNS OF SAID SECOND WINDING BEING CHOSEN SUCH THAT BIAS MAGNETIZATION OF SAID TRANSFORMER CORE IS SUBSTANTIALLY COMPENSATED. 